Method for improving RF spectrum efficiency with repeater backhauls

ABSTRACT

A spectrally efficient wireless communication system that includes a plurality of base stations communicating indirectly with a plurality of wireless communications devices through a plurality of repeaters. The method can generally comprise communicating indirectly between a first base station and a wireless communication device using a first repeater and a first RF backhaul link. A control processor associated with the first base station can control a first smart antenna system. The system selectively configures the first smart antenna system to spatially isolate communications on the first RF backhaul from communications on a second RF backhaul of a second repeater.

RELATED APPLICATION INFORMATION

This is a continuation reissue application of U.S. Reissue ApplicationNo. 12/191,866, filed Aug. 14, 2008 now U.S. Pat. No. Re 42,605, whichis a reissue application of U.S. Pat. No. 7,092,714, issued Aug. 15,2006.

BACKGROUND OF THE INVENTION

1. Technical Field

The inventive arrangements relate generally to mobile telecommunicationssystems and more particularly to a more efficient use of RF spectrumallocation for repeater/base station backhaul links.

2. Description of the Related Art

In a wireless telecommunication system, a base station communicates withmobile communication devices via communication channels, known in theart as ground links. By itself, a base station can only cover a limitedarea with ground links. This limited coverage area is referred to in theart as a cell. Other devices, such as repeaters, are sometimes used toexpand the range of a base station to cover a larger geographic area. Toa limited extent, non-translating repeaters extend the range that a basestation can cover within the same cell. A frequency translating repeatercan provide coverage within the same cell or for a separate cell fromthe cell of its serving base station. Repeaters are typically placedbeyond the range of a base station's ground link so as to expand thebase station's service to cover those cells. A group of cells covered bya base station utilizing repeaters is known a cell cluster. The presentinvention applies generally to the class of repeaters known as frequencytranslating repeaters.

A backhaul communication link allows the base station to communicatewith the repeaters for receiving and transmitting information to/fromthe mobile communications devices. Some base station units and repeatersare configured with a backhaul channel that operate “in band”, i.e. in aportion of the limited frequency spectrum allocated for ground links.Other base stations may support the backhaul in a licensed or unlicensedband other than the band allocated for ground links. However, use of inunlicensed bands is typically undesirable due to interference fromuncontrolled sources. Likewise availability of spectrum in a licensedband other than the band used for ground links may be limited as well ascostly. In conventional systems, a different backhaul carrier frequencyis required for communication between a base station and each associatedfrequency translating repeater. However, in systems that select thebackhaul from a portion of the limited frequency spectrum allocated forground links, such multiple backhaul frequencies reduce the availableground link bandwidth.

A base station may support a number of repeaters that are geographicallydistributed in any direction from the base station. The repeater wouldtypically utilize a narrow beam antenna to receive downlink signals andtransmit uplink signals to its serving base station. This narrow beamantenna focuses transmitted uplink signal to its serving base stationand also limits interference to unintended base stations. However, thebase station typically would employ an omni-directional or broad beamdirectional antenna that could support multiple backhauls to differentgeographically diverse repeaters. Because the downlink (basestation-to-repeater) backhaul is transmitted in a broad direction ratherthan focused to the intended repeater, this broad transmission generatesinterference for unintended repeaters thus limiting spectral efficiency.Likewise, more power is required to be transmitted than would benecessary than if the base station antenna were using narrow beamwidthantenna. On the uplink the base station may receive a signal from anunintended repeater on the same frequency as an intended repeater.

Smart antenna systems are known in the art as a way for multiplecommunication links to improve spectral efficiency by spatiallyisolating those communications links from each other thus reducinginterference. For example, switched beam systems are available that mayconsist of a plurality of narrow antenna beams arranged in a pattern tocover an omni-directional area. In switched beam systems, each antennarequires one or more dedicated transceivers and transmit amplifierstogether with associated RF cabling. This arrangement permitscommunications between the base station and a plurality of remotetransceivers to occur concurrently on the same frequency, but throughdifferent antennas.

Another smart antenna system is comprised of an array of antennaelements that are used to perform adaptive spatial processing. Thesystem works by electronically forming RF beams and nulls by adjustingthe phase and amplitude of each communication channel through each ofthe antennas in the array. Adaptive spatial signal processing applied toRF signals of each of the antenna elements permits RF energy to befocused to/from a specific direction to/from the same base station, thusreducing interference between remote communication devices on the samefrequency that are spatially separated.

Smart antennas have been applied to support spatial division multipleaccess (SDMA) systems for improving spectral efficiency. These systemsmake use of the spatial separation of remote communication devicesenabling multiple remote devices to communicate with an SDMA basestation on the same frequency. SDMA can be implemented using adaptiveantenna systems or switched beam systems.

Much study has been performed to apply SDMA to mobile networks; however,thus far in practice, SDMA systems have been limited to fixed wirelessnetworks, such as wireless local loop (WLL) systems, due to thetremendous computation power required to track a large number of mobilesand monitoring spatial separation of those on the same frequency toprevent unacceptable degradation in signal quality.

Smart antennas have been applied to improve spectral efficiency byreduction of interference allowing higher frequency reuse across amobile network. Each cell in a cell cluster may use unique RFfrequencies for that cell; however, those RF frequencies may be reusedin cells of another cell cluster. By reducing interference through theuse of smart antennas, cells of different clusters using the samefrequencies may be placed geographically closer, allowing thosefrequencies to be used more often, thus improving spectral efficiency.

Hence, in a network making use of frequency translating repeaters, whatis needed is a mobile communication system that can take advantage ofexisting smart antenna technology for more efficient use of frequencyspectrum, in particular the loss of spectral efficiency due to the useof backhaul communication channels.

SUMMARY OF THE INVENTION

The invention concerns a method and system for implementing a morespectrally efficient wireless communication system that includes aplurality of base stations communicating indirectly with a plurality ofwireless communications devices through a plurality of repeaters. Themethod can generally comprise communicating indirectly between a firstbase station and a wireless communication device using a first repeaterand a first RF backhaul link. A control processor associated with thefirst base station can control a first smart antenna system. The systemselectively configures the first smart antenna system to spatiallyisolate communications on the first RF backhaul from communications on asecond RF backhaul of a second repeater.

The first base station can communicate with a second wirelesscommunication device using the second repeater and the second RFbackhaul link. Alternatively, the second repeater can communicate with asecond base station located in a communication cell separate from thefirst base station. In the latter case, the method can further includethe steps of selectively controlling a second smart antenna system ofthe second base station for improved spectral efficiency. Specifically,this can be accomplished by selectively configuring the second smartantenna system to spatially isolate communications on the second RFbackhaul link from communications on the first RF backhaul link.

The controlling step mentioned above can include the step of selectingfrom an antenna array at least one antenna element for use by the firstbase station in producing a directional antenna pattern having a majorlobe in the direction of the first repeater. According to oneembodiment, the controlling step can further comprise selecting aplurality of antenna elements from the antenna array for use by thefirst base station and adjusting phase and/or amplitude of RF signalsreceived and transmitted by the plurality of antenna elements to producethe directional antenna pattern. Similarly, the controlling step caninvolve selecting a plurality of antenna elements from the antenna arrayfor use by the base station and adjusting at phase and/or amplitude ofRF signals received and transmitted by the plurality of antenna elementsto produce a null in the directional antenna pattern. For example, thenull can be selectively directed toward the second repeater.

According to an alternative embodiment, the invention can comprise afirst base station configured for communicating indirectly with awireless communication device using a first repeater and a first RFbackhaul link. The base station can include a first smart antenna systemoperatively associated with the first base station. The first smartantenna system can be selectively configured by a control processor forspatially isolating communications on the first RF backhaul fromcommunications on a second RF backhaul of a second repeater. The firstbase station can communicate with a second wireless communication deviceusing the second repeater and the second RF backhaul link.Alternatively, the second repeater can be arranged for communicatingwith a second base station located in a communication cell separate fromthe first base station.

The second base station can comprises a second control processor forselectively controlling a second smart antenna system of the second basestation. The second smart antenna system can be arranged for spatiallyisolating communications on the second RF backhaul link fromcommunications on the first RF backhaul link. The control processor canselect from an antenna array at least one antenna element for use by thefirst base station. According to one aspect of the invention, theantenna element or elements can be used to produce a directional antennapattern having a major lobe in the direction of the first repeater.

According to another aspect of the invention, the control processor canselect a plurality of antenna elements from the antenna array for use bythe first base station. In that case, the first smart antenna system caninclude phase and amplitude controllers for adjusting at least one of aphase and amplitude of RF signals received and transmitted by theplurality of antenna elements to produce the directional antennapattern. Similarly, the control processor can select a plurality ofantenna elements from the antenna array for use by the first basestation and the first smart antenna system can include phase andamplitude controllers for adjusting phase and/or amplitude of RF signalsreceived and transmitted by the plurality of antenna elements to producea null in the directional antenna pattern. The null can be selectivelydirected toward the second repeater.

BRIEF DESCRIPTION OF THE DRAWINGS

There are presently shown in the drawings embodiments, which arepresently preferred, it being understood, however, that the invention isnot limited to the precise arrangements and instrumentalities shown.

FIG. 1 shows a simple diagram of a mobile communications networkincorporating a base station and repeaters.

FIG. 2 shows a base station using a switched-beam antenna array tocommunicate with multiple repeaters simultaneously.

FIG. 3 shows a base station using and adaptive antenna array tocommunicate with multiple repeaters simultaneously.

FIG. 4 shows a simplified block diagram of a base station incorporatingsmart antennas.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 is diagram of a mobile communications network 100 incorporatingbase stations 102, repeaters 104, and mobile communication devices 106.Generally, base stations 102 can facilitate communication among mobilecommunication devices 106 and between mobile communication devices 106and other data networks, for example a public switched telephone network(PSTN) 124 or a public switched packet network (PSPN) 125. Signalscommunicated to and from a PSTN or PSPN pass through a mobile telephoneswitching office (MTSO) 120. Base stations 102 can receive communicationsignals from MTSO 120 and modulate the signals to format them fortransmission through base station antennas 110. Base stations 102 canalso receive signals transmitted to base station antennas 110 fromrepeaters 104, or mobile communication units 106. These signals arecommunicated to the MTSO 120. Base station controller 122 canincorporate a management application to manage the operations of aplurality of base stations 102.

Base stations 102 conventionally communicate with mobile communicationdevices 106 via groundlinks. By itself, a base station 102 can onlycover a limited area with groundlinks. This limited coverage area isreferred to in the art as a cell. Hence, repeaters 104 are typicallyplaced in cells outside the reach of a base station's groundlink toexpand the base station's service to cover those cells. A group of cellscovered by a base station 102 and its associated repeaters 104 isreferred to in the art as a cell cluster.

Repeaters 104 can receive communications transmitted from acorresponding base station 102 over a backhaul link and can forward thecommunications to mobile communication devices 106 through antennas 114.Likewise, repeaters 104 can receive communications transmitted frommobile communication devices 106 and forward these communications to thecorresponding base station 102 over the backhaul link through antennas115.

According to a preferred embodiment of the invention, base station 102can incorporate suitable hardware and software for implementing smartantenna processing. Such processing can permit a single frequency to beused for implementing multiple backhaul links between a base station 102and multiple repeaters 104, or for improved frequency re-use in a systemof base stations making use of such smart antennas for implementingrepeater backhaul links. Implementing multiple repeater backhaul linkson the same RF frequencies, either within a cell or among a group ofcells, can be highly advantageous as it increases the availablebandwidth for ground link communications with mobile communicationdevices 106.

Smart antenna processing systems as described herein can includeswitched-beam antenna systems, adaptive antenna processing, or any othersystem incorporating special processing techniques to focus antennapropagation patterns for reducing co-channel or adjacent channelinterference. FIG. 2 shows a base station 102 that incorporates aconventional switched-beam antenna array 211 for communication withmobile units 106 and repeaters 104. The switched-beam antenna array 211comprises 16 antenna elements, each having a 22.5 degree beamwidth, soas to cover a 360 degree propagation angle. However, those skilled inthe art will appreciate that the invention is not limited in thisregard. Rather, the switched-beam antenna array 211 can comprise anyother desired arrangement of multiple narrow beam antennas, each with anindividual antenna pattern 202 covering a narrow azimuth region. As isconventional in such systems, each switched beam antenna associated withantenna array 211 requires a dedicated transceiver and a transmitamplifier together with associated RF cabling. This arrangement permitsa base station to communicate with one or more remote repeaters on thesame backhaul frequency without substantial interference. It can alsopermit base stations in a cell cluster to have improved levels offrequency reuse by allowing a common set of backhaul frequencies to beused more often by different base stations within the cell cluster.

In addition to providing concurrent communications with multiplerepeaters on a single backhaul frequency, the arrangement in FIG. 2 canalso be used to concurrently permit groundlink communications on thesame frequency between a base station 102 and a mobile communicationunit 106. Groundlink communications with a mobile transceiver unit 106can be switched from one antenna element to another as the mobilecommunication unit 106 moves from a region covered by one antennaelement to a region covered by another antenna element.

FIG. 3 illustrates an adaptive antenna type system according to analternative preferred embodiment in which adaptive spatial processing isused to define and steer antenna patterns 302. The geometry of theadaptive array determines spatial resolution of the signals transmittedor received, i.e. the amount of coverage in a given spatial region.Commonly used adaptive array types are the uniform linear and circulararrays. For any given geometry, the phases and amplitudes of thecurrents exciting the array elements as well as the number of arrayelements determine the transmission power of the array in a certaindirection. The phases and amplitudes of the currents on the antennaarray elements can be electronically adjusted using amplitude and phasecontrollers such that transmitted signals in a certain direction add inphase, and maximum power is directed in that direction. Due to thereciprocal nature of adaptive antennas, this approach is also generallyapplicable to enhance the receive gain of an antenna array in aparticular direction as well.

The embodiment of FIG. 3 is similar to that of FIG. 2 except that use ofthe adaptive antenna techniques as opposed to switched-beam antennasmakes the angular positioning of the repeaters 104 around the basestation 102 less critical. More particularly, since adaptive arrayprocessing permits provides greater flexibility in directing the antennapattern 302 in a particular direction as compared to switched-beamantennas, there is greater flexibility in the positioning of therepeaters. Adjacent repeaters 104 need only be separated enough so thateach major lobe pattern 202 does not significantly overlap any two ormore repeaters using the same frequency. Adaptive spatial processing hasthe further advantage in this context of permitting the antenna array tocreate RF nulls in the direction of interfering co-channel signalsoperating on the same frequency. This reduces the strength of undesiredsignals interfering with RF received from a desired repeater. In anycase the adaptive antenna array 311 can permit base station 102 tocommunicate with multiple repeaters 104 on a same backhaul frequency atthe same time without significant interference between the signals. Itcan also allow multiple base stations, which are nearby to one anotherto communicate with multiple repeaters on a same backhaul frequency.

Referring to FIG. 4, base station 102 can have a selected number ofantenna elements 110 in a switched-beam or adaptive array antennasystem. Each antenna element has a dedicated receive apparatus chaincomprising duplexer 520, broadband digital transceiver 540, and achannelizer/combiner 550 (including analog to digital converter). Asuitable interface such as time division multiplex bus 560 can beprovided for facilitation communications between the dedicated receiveapparatus chain and digital signal processor board (DSP) 570. The DSP570 can provide signal processing, for example beam forming (in the caseof adaptive array processing), antenna selection (in the case ofswitched-beam antenna processing), signal modulation, signalcalibration, etc. DSP 570 can include a plurality of individual digitalsignal processors for performing these tasks for each channel.

For transmission, each antenna element 110 has a dedicated transmitapparatus chain comprising duplexer 520, multi-carrier power amplifier(MCPA) 530, broadband digital transceiver 540, combiner 551 (includingdigital to analog coverter), time division multiplex bus 560, DSP 570,and associated connectors inclusive. Similar to its function on thereceive path, DSP 570 can perform antenna switching or adaptive arraybeam forming. DSP 570 can also apply any other desired signal processingto the transmit signals, for example switching transmit signals betweenantenna elements when transmitting through a switched-beam antennaarray.

A control processor 580 can be provided for controlling the operation ofthe major system components including the bus 560, and each channelizer550, combiner 551, broadband digital transceiver 540, MCPA 530. Thecontrol processor can communicate with these system components using acontrol bus 581. Where a switched-beam antenna system is used, thecontrol processor 580 can select one or more antennas 110 to operateexclusively with each of the plurality of repeaters 104, where eachantenna or combination of antennas can having an antenna pattern 202comprising a major lobe exhibiting gain in a direction of one of therepeaters 104. RF signals communicated to and from the base station 102for each of the plurality of repeaters 104 can be processed separatelyin one of the plurality of the transceivers 540 associated with each ofthe antennas.

Alternatively, where an adaptive array approach is used, the controlprocessor 580 can adjusts a phase, amplitude or both for RF signalsassociated with all of the plurality of antennas of the antenna array.These operations can be performed in the channelizer and combiner blocksor within DSP 570. In this way the system can combine the RF signals tocreate an antenna pattern 302 comprising a major lobe exhibiting gain ina direction of one of the plurality of repeaters 104. The controlprocessor 580 can also adjust a phase and/or amplitude of RF signalsassociated with each of the plurality of antennas 110 of the antennaarray for combining the RF signals to create an antenna patterncomprising nulls in the direction of at least one other of the pluralityof repeaters concurrently operating on the common RF carrier frequency.

It should be understood that the examples and embodiments describedherein are for illustrative purposes only and that various modificationsor changes in light thereof will be suggested to persons skilled in theart and are to be included within the spirit and purview of thisapplication. The invention can take many other specific forms withoutdeparting from the spirit or essential attributes thereof for anindication of the scope of the invention.

We claim:
 1. In a wireless communication system with a plurality of basestations communicating indirectly with a plurality of wirelesscommunications devices, a method for more efficient use of radiospectrum, comprising: communicating indirectly between a first basestation and a wireless communication device using a first repeater and afirst RF backhaul link between said first repeater and said first basestation; controlling a first smart antenna system of said first basestation for improved spectral efficiency by selectively configuring saidfirst smart antenna system to spatially isolate communications on saidfirst RF backhaul link from communications on a second RF backhaul linkof a second repeater operating on the same RF carrier frequency as thefirst RF backhaul link.
 2. The method according to claim 1 wherein saidcommunicating step further comprises said first base stationcommunicating with a second wireless communication device using saidsecond repeater and said second RF backhaul link.
 3. The methodaccording to claim 1 wherein said second repeater communicates with asecond base station located in a communication cell separate from saidfirst base station.
 4. The method according to claim 3 furthercomprising selectively controlling a second smart antenna system of saidsecond base station for improved spectral efficiency by selectivelyconfiguring said second smart antenna system to spatially isolatecommunications on said second RF backhaul link from communications onsaid first RF backhaul link.
 5. The method according to claim 1 whereinsaid controlling step further comprises selecting from an antenna arrayat least one antenna element for use by said first base station inproducing a directional antenna pattern having a major lobe in thedirection of said first repeater.
 6. The method according to claim 5wherein said controlling step further comprises selecting a plurality ofantenna elements from said antenna array for use by said first basestation and adjusting at least one of a phase and amplitude of RFsignals received and transmitted by said plurality of antenna elementsto produce said directional antenna pattern.
 7. The method according toclaim 5 wherein said controlling step further comprises selecting aplurality of antenna elements from said antenna array for use by saidbase station and adjusting at least one of a phase and amplitude of RFsignals received and transmitted by said plurality of antenna elementsto produce a null in said directional antenna pattern, said nullselectively directed toward said second repeater.
 8. In a wirelesscommunication system with a plurality of base stations communicatingindirectly with a plurality of wireless communications devices through aplurality of repeaters, a system for providing more efficient use ofradio spectrum, comprising: a first base station configured forcommunicating indirectly with a wireless communication device using afirst repeater and a first RF backhaul link between said first repeaterand said first base station; a first smart antenna system operativelyassociated with said first base station, said first smart antenna systemselectively configured by a control processor for spatially isolatingcommunications on said first RF backhaul link from communications on asecond RF backhaul link of a second repeater operating on the same RFcarrier frequency as the first RF backhaul link.
 9. The system accordingto claim 8 wherein said first base station communicates with a secondwireless communication device using said second repeater and said secondRF backhaul link.
 10. The system according to claim 8 wherein saidsecond repeater communicates with a second base station located in acommunication cell separate from said first base station.
 11. The systemaccording to claim 10 wherein said second base station comprises asecond control processor for selectively controlling a second smartantenna system of said second base station for spatially isolatingcommunications on said second RF backhaul link from communications onsaid first RF backhaul link.
 12. The system according to claim 8 whereinsaid control processor selects from an antenna easy at least one antennaelement for use by said first base station, and said at least oneantenna element produces a directional antenna pattern having a majorlobe in the direction of said first repeater.
 13. The system accordingto claim 12 wherein said control processor selects a plurality ofantenna elements from said antenna array for use by said first basestation and said first smart antenna system includes phase and amplitudecontrollers for adjusting at least one of a phase and amplitude of RFsignals received and transmitted by said plurality of antenna elementsto produce said directional antenna pattern.
 14. The system according toclaim 12 wherein said control processor selects a plurality of antennaelements from said antenna array for use by said first base station andsaid first smart antenna system includes phase and amplitude controllersfor adjusting at least one of a phase and amplitude of RF signalsreceived and transmitted by said plurality of antenna elements toproduce a null in said directional antenna pattern, said nullselectively directed toward said second repeater.
 15. A controlprocessor configured to: spatially isolate communications on a first RFbackhaul link from communications on a second RF backhaul link operatingon a same RF carrier frequency as said first RF backhaul link, whereinsaid control processor is operably coupled to a first smart antennasystem associated with said first base station for providing moreefficient use of radio spectrum, wherein said second RF backhaul link istransmitted via a second repeater, and wherein a first base stationcommunicates indirectly with a wireless communication device using afirst repeater and said first RF backhaul link between said firstrepeater and said first base station.
 16. The control processorconfigured according to claim 15, wherein said first base stationcommunicates with a second wireless communication device using saidsecond repeater and said second RF backhaul link.
 17. The controlprocessor configured according to claim 15, wherein said second repeatercommunicates with a second base station located in a communication cellseparate from said first base station.
 18. The control processorconfigured according to claim 15, further configured to selectivelycontrol a second smart antenna system of said second base station forimproved spectral efficiency by selectively configuring said secondsmart antenna system to spatially isolate communications on said secondRF backhaul link from communications on said first RF backhaul link. 19.The control processor configured according to claim 18, furtherconfigured to select from an antenna array at least one antenna elementfor use by said first base station in producing a directional antennapattern having a major lobe in the direction of said first repeater. 20.The control processor configured according to claim 15, furtherconfigured to select a plurality of antenna elements from an antennaarray for use by said first base station and adjusting at least one of aphase or an amplitude of RF signals received and transmitted by saidplurality of antenna elements to produce a directional antenna pattern.21. The control processor configured according to claim 15, furtherconfigured to select a plurality of antenna elements from an antennaarray for use by said first base station and adjust at least one of aphase or an amplitude of RF signals received and transmitted by saidplurality of antenna elements to produce a null in a directional antennapattern, said null selectively directed toward said second repeater.